This invention relates to switching devices and, more particularly, to switches for networks of devices such as computers employing Ethernet, fiber channel, Asynchronous Transfer Mode, or other networking technology to provide a degree of fault tolerance.
It is well known to connect networks of computing devices such as hosts, printers, servers, etc. with switches that improve network performance by routing packets between pairs of devices that are in communication with each other, rather than over a common medium, which requires all devices to receive all packets.
Switches, such as Ethernet switches, allow simultaneous connections between pairs of devices on a network and greatly improve the bandwidth of a network compared with non-switching techniques, such as hubs which use a physically or logically common medium.
Network switches commonly employed have a relatively small number of ports (4-64), each of which is connected to a single network segment. Since each network segment shares a common access medium, the number of devices on each switch segment is usually kept as small as practical. Where more devices are connected to a network, multiple interconnected switches are commonly used. Typically, the connections between the switches operate at a higher speed than the switch ports to improve network performance.
In a network of the type described above, the failure of a single switch renders the network unavailable to all of the devices connected to that switch. For example, if a network switch fails, all of the devices attached to that switch are disconnected from the network until the switch is replaced. Network switches typically include components such as printed circuit boards, on which logical devices are mounted, power supplies, and other components, the failure of any one of which can render the entire switch inoperable. These so-called single point of failure network interruptions are very disruptive and expensive and improving the reliability of switches has become critically important.
Many general purpose techniques for improving reliability have been applied to network switches. Providing redundant critical components is a commonly used approach and can overcome some of the single point of failure problems. For example, a network switch can be provided with redundant power supplies, cooling systems, and even switching circuits so that, upon the failure of one component, another component is automatically switched into place so that the switch continues to operate. It is a significant disadvantage of redundant fault protection of the type just described that it increases the cost of network switches without improving switching performance. Providing redundant power supplies, for example, involves the cost of providing a second power supply, which is almost never used, together with the circuitry for switching between a failed power supply and the backup power supply. Configuring the network switch so that the failed component can be replaced without interrupting its operation also adds cost and complexity. This type of redundancy is so expensive that its application is not justified except in situations where reliability is sufficiently critical that the excess cost is acceptable.
It is an object of the present invention to provide a fault tolerant switching arrangement that overcomes some of the disadvantages just mentioned.
The present invention is meant to offer a very cost effective and practical solution for improving reliability in communications, for example, in an Ethernet network.
It is a particular object of the present invention to provide a fault tolerant network switch that includes two or more switches units and a highly reliable (i.e., one with no single point of failure) interconnect unit so that during normal operation both switches are actively handling network packets and upon the failure of one of the switch units, another switch unit takes over, ensuring continued normal network operation, possibly with somewhat reduced performance. The failed switch unit can then be replaced and the network returned to its original performance without disturbance to the other switch or the network cable connections.
Briefly stated and in accordance with a presently preferred embodiment of the invention, a fault tolerant switch comprises two or more switch units, each having a plurality of switched ports and a hub having at least two ports connected to each switched port. Each switch unit is connected to an interconnect unit connecting each network segment to two or more of the hub ports on the two switch units.
In accordance with a particularly preferred embodiment of the invention, a fault tolerant network switch includes a first switching controller having a plurality of switched ports, a first hub connected to one of the plurality of switched ports and a plurality of independently connectable network ports, each connected to the hub, the connectable network ports having two states, a normal state in which one of the network ports is connected to the hub, and a survivor state in which two or more of the network ports are connected to the hub, and a second switching controller having a plurality of switched ports, a second hub connected to one of the plurality of switched ports, and a plurality of independently connectable network ports connected to the hub, the connectable network ports of the second switching controller having two states, a normal state in which one of the network ports is connected to the hub, and a survivor state in which two or more of the network ports are connected to the hub, and a plurality of network connectors, each of which is connected in parallel to the network ports associated with each of the first and second hubs.
In accordance with another aspect of the invention, each of the switch units includes a fault detector for monitoring the operation of the switch unit and, upon a fault, immediately communicating this status information to the fault detector of another switch unit.
In accordance with another aspect of the invention, status information from the fault detector of one of the switch units is used within the same switch unit to change the state of the independently connected network ports.
In accordance with another aspect of this invention, further redundancy is provided by having a third switching controller also having a plurality of switched ports, a third hub connected to one of the plurality of switched ports, and a plurality of independently connectable network ports connected to the third hub, the connectable network ports having two states, a normal state in which one of the networks is connected to the hub, and a survivor state in which two or more of the network ports are connected to the hub.
In accordance with another aspect of the invention, an interconnect unit for connecting a plurality of network switch units to a plurality of network ports includes a first multi-port connector adapted to be connected to a first network switch unit, a second multiport connector adapted to be connected to a second network switch unit, and a plurality of single port network connectors, each of which is connected in parallel to both the first and second connectors, the interconnect unit not including any single component, the failure of which affects more than one network port.
In accordance with a further embodiment of the invention, the interconnect unit includes a plurality of isolation switches, each isolation switch connected to a network port of one of the first and second network switch units by way of one of the multiport connectors, for isolating the network port from the first and second connectors, the isolation switches being configured so that a failure of any isolation switch does not affect any other isolation switch.
In accordance with a still further embodiment of the invention, a network switch unit includes a switching controller having a plurality of switched ports, a two state hub connected to one of the plurality of switched ports and having a plurality of network ports, the hub having two states, a normal state in which one of the network ports is connected to the switched port and a survivor state in which two or more of the network ports are connected to the switched port.
In accordance with another aspect of the invention, the network switch unit includes a fault detector for providing a fault signal upon detecting a fault in the network switch unit.
In accordance with another aspect of the invention, the network switch unit includes a control input for receiving a fault signal from another network switch unit.
In accordance with still another aspect of the invention, the two state hub of a network switch unit are connected to the fault detector of that same network switch unit.
In accordance with yet another aspect of the invention, the hub has a third, failure state, in which none of the network ports is connected to the switched port.
A significant advantage of the fault tolerant network switch is nonstop performance at a modest system price, making fault tolerant network switching an affordable solution for both small and large networks. Unlike conventional fault tolerant implementations, all switch components are active under normal conditions.
The present invention embodies two or more switching units with an interface unit arranged in such a way that none of the cabling is disturbed when a switching unit is replaced. The present invention relates to a fault tolerant switch in which fault tolerance is provided for a single point of failure.
In an embodiment of the fault tolerant switch of the present invention, two identical switch units each detect faults internally and relay the status to the other switch unit.